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I have a high idle due to the computer keeping the Idle Air Control valve staying open letting the air go past the MAF sensor. I have smoke tested the car with my home made smoke maker. After getting the engine warm the IAC valve still lets air in bypassing the MAF sensor. I put a new IAC valve just to make sure it wasn't the valve. A wells youtube diagnostic video showed the 4 wire connector giving off electricity on all of the connectors when the engine was running. At warm engine mine shows the two outside wires of the connector as hot but not the two inner ones. I have an older 90's diagram in my Chiltons showing the 4 wires. Would this be good enough for my testing? It shows the wire going from the harness all the way back to the computer. I was wondering if I should test for continuity on the two blank wires all the way back to the computer. I don't see a harness where I could test them midway. Anyone have an electrical diagram more up to date than mine? I was thinking of going to alldata with a subscription for the wiring diagram. Also my MAF sensor reads 5 to 5.5 g/sec. Isn't that a high reading? Unfortunately it is an older Autozone sensor not AC Delco. I have no codes now (had a single P0507) but have a high long term fuel trim (16) due to the IAC being open. I need the car smogged in the next 3 weeks so any suggestion would be helpful.
 

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The IAC doesn't bypass the MAF sensor, it is after that, and opens a small path above the closed throttle blade to permit a small amount of air for idling. The wiring was the same over the entire Series 2 era, as you can swap them between cars with 3800, Northstar, and LS1 throttle bodies without hassle (TPS was the only sensor that had different versions for the V8's).

High LTFT means your car is trying to add fuel due to a lean reading by the front oxygen sensor. I haven't seen this issue recently, but it doesn't sound out of the ordinary. You can try checking again for vacuum leaks with tubing as a stethoscope to help hear anything around the top of the engine. If it's not stumbling or struggling to hold normal RPM at idle, it seems like there's extra air coming in somewhere else.

Hope that gives you some more threads to pull.
 

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The IAC doesn't bypass the MAF sensor, it is after that, and opens a small path above the closed throttle blade to permit a small amount of air for idling. The wiring was the same over the entire Series 2 era, as you can swap them between cars with 3800, Northstar, and LS1 throttle bodies without hassle (TPS was the only sensor that had different versions for the V8's).

High LTFT means your car is trying to add fuel due to a lean reading by the front oxygen sensor. I haven't seen this issue recently, but it doesn't sound out of the ordinary. You can try checking again for vacuum leaks with tubing as a stethoscope to help hear anything around the top of the engine. If it's not stumbling or struggling to hold normal ROM idle, it seems like there's extra air coming in somewhere else.

Hope that gives you some more threads to pull.
The IAC doesn't bypass the MAF sensor, it is after that, and opens a small path above the closed throttle blade to permit a small amount of air for idling. The wiring was the same over the entire Series 2 era, as you can swap them between cars with 3800, Northstar, and LS1 throttle bodies without hassle (TPS was the only sensor that had different versions for the V8's).

High LTFT means your car is trying to add fuel due to a lean reading by the front oxygen sensor. I haven't seen this issue recently, but it doesn't sound out of the ordinary. You can try checking again for vacuum leaks with tubing as a stethoscope to help hear anything around the top of the engine. If it's not stumbling or struggling to hold normal ROM idle, it seems like there's extra air coming in somewhere else.

Hope that gives you some more threads to pull.
I feel like $.010. I tried to adjust the new IAC sensor to right at 1.125 in. As I did so the old sensor tipped over and the plunger fell out. After 230K it unscrewed itself. Never thought to check the plunger to see if it unscrewed itself. I readjusted the old one and installed it. It still reads 940 rpm at idle. However it goes to 740 rpm vs 625 desired when in drive or reverse. The engine is on the money when I turn on the air conditioning and it matches engine rpm to a t. Thanks for the advice Dave. I do have an exhaust leak in secondary air connector behind the back side of the engine. Hopefully I will fix that tomorrow and will see if that helps my idle. You can see the IAT still open when the engine is warm.
 

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Glad you're seeing improvement. Keep us posted, in case someone else can benefit from the story and results.
 

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I have a high idle due to the computer keeping the Idle Air Control valve staying open letting the air go past the MAF sensor. I have smoke tested the car with my home made smoke maker. After getting the engine warm the IAC valve still lets air in bypassing the MAF sensor. I put a new IAC valve just to make sure it wasn't the valve. A wells youtube diagnostic video showed the 4 wire connector giving off electricity on all of the connectors when the engine was running. At warm engine mine shows the two outside wires of the connector as hot but not the two inner ones. I have an older 90's diagram in my Chiltons showing the 4 wires. Would this be good enough for my testing? It shows the wire going from the harness all the way back to the computer. I was wondering if I should test for continuity on the two blank wires all the way back to the computer. I don't see a harness where I could test them midway. Anyone have an electrical diagram more up to date than mine? I was thinking of going to alldata with a subscription for the wiring diagram. Also my MAF sensor reads 5 to 5.5 g/sec. Isn't that a high reading? Unfortunately it is an older Autozone sensor not AC Delco. I have no codes now (had a single P0507) but have a high long term fuel trim (16) due to the IAC being open. I need the car smogged in the next 3 weeks so any suggestion would be helpful.
Yup, ALLDATA has the best and most accurate info as well as diagrams. We use this almost every day at our shop. Accurate info and normally good diagrams(with wire colors). Being in the auto service industry for MANY YEARS, I think alldata is the BEST and most accurate. Good luck, Jake(mr goodwrench).....
 

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Discussion Starter #6
Yup, ALLDATA has the best and most accurate info as well as diagrams. We use this almost every day at our shop. Accurate info and normally good diagrams(with wire colors). Being in the auto service industry for MANY YEARS, I think alldata is the BEST and most accurate. Good luck, Jake(mr goodwrench).....
Thanks for the advice Jake. Have you ever had the situation of the IAC valve working perfectly with the desired idle rpm (DI). But the rpm was 125 rpm higher than DI just in drive. I do have a leak in my secondary air piping I am fixing but I am perplexed by the perfect response with air conditioning only. Does the AC have it's own ground? I haven't ever reshined the grounds on the buick.
 

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Your IAC might be trying to let in air normally, but the leak's extra air causes the idle to increase slightly. The load of the A/C may demand more air to support the commanded RPM, so this leak just means the IAC is being 'helped' accidentally.
 

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Yup, ALLDATA has the best and most accurate info as well as diagrams. We use this almost every day at our shop. Accurate info and normally good diagrams(with wire colors). Being in the auto service industry for MANY YEARS, I think alldata is the BEST and most accurate. Good luck, Jake(mr goodwrench).....
PS, with that high idle issue, one would think the PCM should have set a DIAG CODE to follow. That said, do you have a check engine light coming on? I just dawned on me your IAC may not be functioning properly. I would not normally suggest this but......in days gone by I have pulled IAC's off and using choke and carb cleaner got rid of all the gunk and manually pushed and pulled the IAC pental shaft in and out while rinsing with the carb/choke cleaner. That usually gets the IAC back to working condition......but keep in mind the IAC can fail in which case you will be off the the auto parts store. HEY, let us know how this all goes for you. PS, do you have access to a GOOD DIAGNOSTIC SCANNER??
 

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Discussion Starter #9
PS, with that high idle issue, one would think the PCM should have set a DIAG CODE to follow. That said, do you have a check engine light coming on? I just dawned on me your IAC may not be functioning properly. I would not normally suggest this but......in days gone by I have pulled IAC's off and using choke and carb cleaner got rid of all the gunk and manually pushed and pulled the IAC pental shaft in and out while rinsing with the carb/choke cleaner. That usually gets the IAC back to working condition......but keep in mind the IAC can fail in which case you will be off the the auto parts store. HEY, let us know how this all goes for you. PS, do you have access to a GOOD DIAGNOSTIC SCANNER??
Cool! I never thought of rinsing the IAC valve. As you saw from above the pintle dropped out from being unscrewed for all its' usage. I will have to wash it up. I have no codes. I have a blue drive, auto x ray (old) my favorite but just conked out, I have a launch 123 series that does engine, transmission, antilock brake, and air bag codes. The weird thing is when I go for drive it takes forever to get to a lean high long term fuel trim (+15). What is wild is I will be going 55 down the freeway and when I let off the gas the LTFT goes from 4 to 15 in a fraction of a second. I once got the infamous P0507. Cleared it and it never came back. Now mostly the idle is 125 rpm higher than desired. One other question Jake, Scanner Danner said that a rule of thumb is that the MAF reading at idle is usually 1g/Liter of engine. My MAF is reading 5-5.5g/sec. It is an autozone special. I know I should have only got ac delco, but that was what was handy 9 years ago. I have heard a lot of people using the Hitachi MAF and being quite happy with it. Have you had any experience with Hitachi? My O2 sensors are Denso. I love Denso products. Anyway tell me what you think of the MAF reading. I can get a new MAF since it had a life time warranty. First I am going to fix this leak before I do anything else. Thanks for the help.
 

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Hitachi makes the OEM MAF. Denso O2's are great, I run them on my turbo car to even handle a little 110 leaded (always carry a spare in case, but it's worth the 'boost' for track/dyno).

If you're getting extra air from a leak, the LTFT's will increase fuel to compensate. That makes sense. Feel free to look into deleting the AIR injection system, or repairing the leak, at least, and your issues should decrease.
 
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